Suction excavator

ABSTRACT

A suction excavator including an air pump for generating a flow of air and a nozzle through which air is drawn under the influence of the air pump, the nozzle being arranged when in use to suck up spoil from an excavation, and a mechanism for separating spoil from the air drawn through the nozzle. The excavator is provided with a fuel gas detector to detect for the presence of fuel gas in the flow of air drawn up through the nozzle. When fuel gas is detected a valve may be actuated to interrupt the flow of air up through the nozzle and instead to admit air from a substantially fuel gas free source to flush any fuel gas out of the system reducing the risk of an explosion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for excavating a hole bysucking debris and spoil out of the

2. Discussion of Background

Such an apparatus is shown for example in German utility model DE29902562 U1 which discloses a vehicle with a suction tube to be insertedinto a hole or excavation to suck debris and spoil out of the hole, anair pump to cause the suction and a filter to remove the spoil from theairflow.

Excavating holes using a suction excavator as in the above Germanutility model is advantageous because holes with a much smallerhorizontal cross-section can be dug using this device than previousexcavations made using drills, spades etc. Excavating using a suctionexcavator is much quicker than conventional digging techniques, reducesthe amount of spoil produced from the hole and the amount of tarmacrequired to re-fill the hole, causes less damage to tree roots and toother utility pipes and cables and causes much less disruption topedestrians and drivers if used in a street. However, because of thelarge volume of air that is sucked through the vehicle, any fuel gasfrom a leaking gas main for example is likely to be sucked into thevehicle. Any sparks produced within the vehicle, for example from theair pump or static build-up within the vehicle due to the fast movementof air through pipes etc., is likely to cause a spark, igniting the gasand causing an explosion.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided asuction excavator with a gas sensor arranged to detect for the presenceof gas in the passage of air through the suction excavator.

The provision of a gas sensor within the suction excavator enables thepresence of potentially dangerous explosive gas within the suctionexcavator to be determined so that appropriate action can be taken.

There is preferably provided a control means which when gas is detectedflushes air through the suction excavator.

All of the components of the suction excavator through which suction airis passed, such as the air pump, suction tube etc., are preferablyelectrically bonded to each other and a connection between the connectedcomponents and earth provided to discharge any electrostatic chargebuilt-up. The bonded components may be connected to earth viaelectrostatically conducting tyres when the suction excavator is mountedon a vehicle or via an electrically conducting strap, for example.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

An example of a vacuum excavator according to the present invention isshown in the accompanying drawings in which:

FIG. 1 shows an operator excavating a hole by directing the nozzle of asuction tube into the hole;

FIG. 2 diagrammatically shows some elements of the suction excavator;

FIG. 3 shows a hopper arranged to receive spoil from the excavation;

FIG. 4 shows a control system connected to a gas sensor of the suctionexcavator; and

FIG. 5 is a flow diagram showing operation of the control system shownin FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an excavation 10 which may for example be made to reach asubterranean pipe or cable. When in urban areas and the excavation ismade into a road or a pavement, a pneumatic drill may initially be usedto break into the hard tarmac surface of the ground. A nozzle 11 isconnected to an air pump and a filtering unit, which in this case aremounted on a vehicle 12. The nozzle 11 is used to suck up spoil from theexcavation 10. If necessary whilst sucking up spoil through nozzle 11the ground in the excavation 10 may be broken up using, for example, apole, a spade, a fork, or more preferably an air knife as is well knownin the art for delivering a high velocity jet of air. This suctionnozzle 11 has a circular cross section of about 25 cm diameter and inthis case the periphery of the tip of the nozzle 13 follows anundulating path which is less likely to damage subterranean pipes whichthe free end of the nozzle 11 may encounter. The nozzle 11 is providedwith couplings or brackets 14 into which any number of extension pipes15 may be inserted to extend the length of the nozzle 11. In thisexample the nozzle is made from aluminium which is strong and light. Thenozzle is provided with an on/off switch, in this case on a handle 16used by the operator to direct the nozzle. The on/off switch immediatelystarts/continues or stops suction through the nozzle 11. The switch ispreferably arranged such that an operator must constantly apply pressureto it to continue the sucking operation. When the operator stopsapplying pressure to the switch suction is then immediately stopped. Theability to immediately disengage suction is particularly useful toenable blockages to be cleared from the end of the nozzle and to preventinjury in case the operator or his clothes are accidentally caught inthe nozzle. The nozzle is provided with a flexible hose 17 which may bemade from heavy duty rubber to connect the nozzle to a boom 18 which maybe hydraulically supported for easy operation and which is mounted onthe vehicle 12 containing the air pump and filtering equipment.

FIG. 2 diagramatically shows an example of the suction and filteringequipment. Suction air and entrained spoil is passed from the nozzle 11shown in FIG. 1 through boom 18 to a hopper 20, in this case a drop boxhopper, to remove the vast majority of the spoil entrained in thesuction air. The suction air then passes to a cyclone 30 where it isaccelerated and then to a filter 40 where dust and smaller particles areremoved from the air. The air then passes through an air pump 50 whichin the present example is arranged to pump between 1100 and 1900 cubicmetres of air per minute, and suction air is then discharged throughexhaust system 60 which includes one or more silencers.

FIG. 3 shows the drop box hopper 20 in more detail. Suction air ispassed from boom 18 into the hopper 20 past a gas sensor 21 as is wellknown in the art. Spoil entrained in the incoming air falls under theinfluence of gravity to the bottom of the hopper 22 where it iscollected. The base 23 of the hopper is hinged along one edge 24 and isarranged such that when a particular weight of spoil 22 has accumulatedat the bottom of the hopper 20 the base 23 rotates about a hinge alongthe edge 24 to pass the spoil 22 down a chute 25 for collection ordisposal. The base plate 23 is urged upwardly when in use by the passageof the suction air and is only lowered when the weight of spoil exceedsthe upward force provided by the suction air. If desired acounter-balance 26 may be provided on the hinged base 23 to adjust theweight of spoil that causes its ejection down chute 25.

The substantially spoil-free air passes out of the hopper 20 through aconduit 27 to cyclone 40. Conduit 27 is provided with a valve 28 andvalve actuator 29 arranged, when actuated, to block the passage of airfrom hopper 20 to conduit 27 and instead admit air from outside intoconduit 27, in this case via conduit 27 a. When not actuated, the valve28 admits air from hopper 20 into conduit 27 and blocks the passage ofair from conduit 27 a into conduit 27.

The air from conduit 27 is then sucked through a cyclone 30, as is wellknown in the art, to accelerate the air and then to a filter 40 as isalso well known in the art to remove any dust from the suction air. Thefilter 40 may be regularly cleaned to prevent dust from causing cloggingand preventing the passage of air therethrough.

Air from the filter 40 is sucked to the air pump 50 which is preferablypowered by the gearbox of the vehicle 12 upon which the air pump andfiltering equipment is mounted.

Air from the pump 50 is then passed to silencers 60 as are well known inthe art to vent the air and reduce noise.

FIG. 4 shows a control system including a control means 70 such as amicroprocessor for receiving a signal from gas detector 21. When asignal is received by control means 70 indicating that gas detector 21has detected explosive gas or a predetermined amount of explosive gas inthe boom 18, control means 70 instructs valve actuator 29 to open valve28 thereby preventing the further suction of air from excavation 10.Instead air is drawn from conduit 27 a which is in communication withfresh air, for example from above the vehicle 12 to pass the fresh airthrough the cyclone 30, filter 40, air pump 50 and exhaust system 60thereby flushing out any fuel gas. A further gas sensor 51 is preferablyprovided at the suction air inlet of the air pump 50, the actuation ofwhich also opens valve 28 to prevent the further suction of air from thenozzle 11 and instead flushes clean air through the suction excavationsystem. An audible or visual alarm is preferably activated when a gasdetector 21, 51 is activated to advise an operator of the reason for theinterruption in suction from the nozzle. In order to reactivate thesuction excavation system, a manual re-set 71 must be activated toensure that the operator is aware of the situation. However, the manualre-set 71 will not close valve 28 until the fuel gas concentrationdetected by sensor 21, and if used also sensor 51, has fallen below thepredetermined level which caused its actuation.

FIG. 5 shows the operation of the control system. The control means 70continually monitors gas sensors 21 and 51 to see whether apredetermined concentration of explosive gas has been detected. As soonas a predetermined concentration of explosive gas is detected fromeither sensor, valve 28 is opened and is not closed to permit furthersuction excavation until the concentration of explosive gas has fallenbelow the predetermined level and the manual re-set 71 has beenactivated. The control means 70 preferably continually monitors theconcentration of gas detected by the gas sensors 21, 51 and may storethe received concentrations, for example on a data logger such as a RAMof a computer for subsequent analysis. The control means 70 may be setto open valve 28 when any predetermined gas concentration is detected,for example 1% fuel gas in air. The gas sensors 21, 51 and control means70 are preferably calibrated so that a particular signal from a gassensor 21, 51 corresponds to a known concentration of gas.

The on/off switch to be engaged by the operator and which in this caseis mounted on the operator's handle 16, shuts off suction by openingvalve 27 which provides a much faster shut off than turning off the airpump 50 for example which would take time to slow down through inertia.However, the operator's on/off switch mounted in this case on handle 16cannot override the opening of valve 28 as a result of a signal from agas sensor 21, 51.

Since the movement of air through the components of the suctionexcavation system may generate static charge, this raises thepossibility of sparks being generated which could possibly cause anexplosion, especially if explosive gas is present. To prevent this, eachcomponent through which air is passed by the suction system iselectrically bonded to each other to enable electrostatic charges topass therebetween and the system is connected to earth, for example, viaelectrostatically conducting tyres or via an electrostaticallyconducting strap connected from the system to earth.

If desired, the control means 70 may be arranged to open valve 28 whenany number of potentially explosive situations arise such as anoverheating engine or drive belt or dangerously low oil levels. Againthe manual reset will not be able to close the valve until the cause ofthe opening of the valve 27 has been rectified.

What is claimed is:
 1. An excavating apparatus comprising: an air pumpfor generating flow of air; a nozzle through which air is drawn underthe influence of the air pump, the nozzle being arranged when in use tosuck up spoil from an excavation site; and means for separating spoilfrom the air drawn through the nozzle, wherein a fuel gas sensor isprovided to detect for the presence of fuel gas in the flow of air drawnthrough the nozzle.
 2. The excavating apparatus according to claim 1,wherein a valve is provided which when actuated is arranged to interruptthe passage of air through the nozzle.
 3. The excavating apparatusaccording to claim 2, wherein a control means is provided to actuate thevalve when the fuel gas sensor detects the presence of fuel gas in theair drawn through the nozzle.
 4. The excavating apparatus according toclaim 3, wherein the apparatus is provided with an inlet arranged toreceive air which is substantially free from fuel gas and when thecontrol means actuates the valve to interrupt the passage of air throughthe nozzle, air is instead drawn from the inlet to the air pump whichcontinues operating so that air which is substantially free from fuelgas is flushed through the air pump.
 5. The excavating apparatusaccording to claim 3, wherein the fuel gas sensor is arranged to detectthe concentration of fuel gas in the flow of air drawn through thenozzle and the control means is arranged to actuate the valve when theconcentration of fuel gas detected exceeds a predetermined value.
 6. Theexcavating apparatus according to claim 3, wherein the control means isarranged to keep the valve actuated until a manual reset is activatedand fuel gas is no longer detected by the fuel gas sensor or the fuelgas concentration detected has fallen below the predetermine value. 7.The excavating apparatus according to claim 2, wherein the nozzle isprovided with a switch arranged to be controlled by an operator toactuate the valve to start and stop suction through the nozzle whendesired.
 8. The excavating apparatus according to claim 7, wherein theswitch is arranged such that suction through the nozzle only occurswhile pressure is applied to the switch.
 9. The excavating apparatusaccording to claim 1, wherein the fuel gas sensor is provided in thesuction path between the inlet of the nozzle and the separating means.10. The excavating apparatus according to claim 9, wherein a second fuelgas sensor is provided in the suction path at an inlet to the air pump.11. The excavating apparatus according to claim 1, wherein theseparation means and the air pump are electrically connected to eachother and to earth.
 12. The excavating apparatus according to claim 11,wherein components of the apparatus through which air is passed,including the air pump, a flexible hose, extension pipes, and thenozzle, are also electrically connected to the separating means and theair pump.